1. Field of the Invention
The present invention relates in general to data storage systems such as disk drives. This invention relates in particular to a head gimbal assembly for use in magnetic and magneto-optical data storage systems to enable the writing of data to a magnetic data storage medium with the assistance of laser generated thermal energy. The thermally assisted magnetic writing of data on the storage medium significantly improves the thermal stability of the recorded data. More specifically, the invention relates to the design, fabrication and mounting of the laser assembly in order to couple the laser light to a waveguide which directs the light to the storage medium.
2. Description of Related Art
A conventional magnetic storage system typically includes a magnetic head that has a slider element and a magnetic read/write element, and which is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
Flying head designs have been proposed for use with optical and magneto-optical (MO) storage technology. One motivation for using the magneto-optical technology stems from the availability of higher areal density with magneto-optical storage disks than magnetic storage disks. However, despite the historically higher areal storage density available for magneto-optical disks drives, the conventional magneto-optical disk drive volumetric storage capacity rate of increase has generally not kept pace with the rate of increase of the volumetric storage capacity of magnetic disk drives. One limiting factor in conventional optical reading heads is the low signal to noise ratio exhibited by such heads at high data transfer rates.
Another limiting factor is that optical reading heads could require several optical components such as a laser, lenses, optical fibers, mirrors, and quarter wave plates. Besides the cost of these components, extensive alignment is required, rendering the design, manufacturing, and assembly of optical heads significantly more complex and costly than conventional magnetic heads.
Certain optical or magneto optical head designs mount the laser source either directly on the slider or remotely using an optical fiber and/or lenses to carry the laser beam to the disk. While mounting the laser source directly onto the slider can eliminate some components, this mounting approach could create a problem of stored heat generated by the laser. The slider does not provide a good heat sink for the laser generated thermal energy. This is important because current lasers become damaged if the temperature exceeds approximately 60xc2x0 C. Since many drive temperatures during operation can easily reach 50xc2x0 C. without the addition of the laser source, there is inadequate margin to accommodate the increase in temperature caused by the operation of the laser source.
An additional disadvantage of various optical and magneto optical heads is that the added mass of the optical components result in added seek time.
A further drawback of some optical and magneto optical heads is the added space required to mount the optical components in order to direct and focus the laser beam on the disk. This typically results in increased disk spacing or limiting the drive design to a single disk.
In addition to its cost, the use of an optical fiber to carry the light from the laser to a lens or waveguide necessitates alignment on both ends of the optical fiber.
Further, the use of an optical fiber attached to a slider on one end and coupled to a remote laser source at its other end adds pitch and roll variation and pitch and roll stiffness to the head gimbal assembly, resulting in greater flying height variation. This, in turn, decreases yield, control of performance, and reliability.
Still, other factors that limit the writing (or recording) on a magnetic disk at high data transfer rates (or frequencies) using conventional magnetic heads are the increasing requirements for higher magnetic fields and field gradients to achieve smaller and smaller bit size. High magnetic fields are difficult to achieve particularly with narrow tracks and miniaturized heads.
Therefore, there is still a long felt and still unsatisfied need for a read/write head which is structurally significantly less complex than conventional optical devices. The head requires a minimal number of optical components and minimal optical alignment. It can write at higher track densities and has better control of the data and servo tracks than conventional magnetic heads.
One aspect of the present invention is the use of a magnetic reading element of high track density, combined with a laser heating, thermally assisted write element as is generally defined in patent applications Ser. Nos. 09/005,914 and 09/248,766. The read/write head is capable of high density recording with a high signal to noise ratio with a design which lends itself to mass production.
Another aspect of the present invention is the use of an integrated optical waveguide and a magnetic write element (collectively referred to herein as thermally assisted write element). This thermally assisted write element is fabricated by forming an optical waveguide within the magnetic write gap of the slider using standard wafer fabrication processes.
Important features of this invention reside in the mounting of the laser diode to the head gimbal assembly. The laser diode is attached to a small silicon chip which, in turn, is mounted to the suspension, for example the flexure. The silicon chip serves not only as a mounting block to the suspension but, due to its high thermal conductivity, it also serves as a first stage heat sink, conducting heat away from the laser diode and into the stainless steel suspension. The silicon mounting block also serves as the anode connection for the laser.
Another important aspect of the laser mounting is that, although it is attached to the suspension, it is positioned in close proximity to the backside of the slider, without making contact therewith, and the laser emitter is aligned to the input end of the optical waveguide such that the laser beam is coupled directly to the optical waveguide, eliminating the need of other components such as optical fibers or lenses. The waveguide directs the laser beam onto a target spot on, or within the data storage medium.
Other important aspects of the design lie in the fabrication of an optical coupling device that includes the laser assembly of the present invention. A unique aspect of the laser assembly lies in the silicon mounting blocks. The silicon mounting blocks are produced via conventional deep etch processes. The individual blocks are formed in the silicon wafer and left in the array in xe2x80x9cbreakaway formxe2x80x9d. The laser diodes are soldered to the mounting blocks, xe2x80x9cburned inxe2x80x9d and tested. A wire is die bonded between the laser diode cathode surface and the silicon mounting block anode surface, to serve first as shorting protection against electro-static discharge (ESD) and later to be cut in half and bonded to the Laser power supply circuitry.
An important aspect of the mounting blocks being made from silicon in addition to the production efficiency of the wafer process, is the high thermal conductivity of silicon which serves a critical function of conducting heat away from the laser diode and into the suspension.
The foregoing and other features of the present invention are realized by this read/write head design which is structurally significantly less complex than conventional optical devices, that requires minimal additional optical components and minimal optical alignment, that can write at higher track densities, and that has a good control of the data and servo tracks. The read/write head uses a laser coupled directly to a waveguide, which is integral with the slider, to heat the medium for lowering its coercivity during the write function. The lowered medium coercivity, caused by laser heating allows a relatively weak magnetic field to be used to write data, which upon cooling to ambient temperature becomes magnetically hard and resistant to self erasure over time. The direct coupling of the laser to the waveguide is an important consideration for eliminating costly components and alignments.